import java.util.Scanner; public class No143 { public static void main(String[] args) { // TODO Auto-generated method stub Scanner sc = new Scanner(System.in); int K = sc.nextInt(); int N = sc.nextInt(); int F = sc.nextInt(); int sum=K*N; for(int i=0; i=0) System.out.println(sum); else System.out.println(-1); } }